Maternal education and the intergenerational transmission of birthweight: Evidence from Japan

Birthweight is a key indicator of health capital, influencing long-term outcomes such as education, income, and adult health. Previous studies have examined both its determinants and consequences, showing that low birthweight is associated with poor health, limited schooling, and lower socioeconomic status later in life. However, the pathways of birthweight's intergenerational transmission remain insufficiently understood, particularly the mediating role of maternal education. Moreover, most existing evidence comes from Western countries, and little is known about these mechanisms in Japan, where delayed childbirth and infertility treatments are increasingly common.

We conducted an original survey of Japanese mothers, collecting data on their own birthweight, their children's birthweight, and socioeconomic attributes. Using Structural Equation Modeling (SEM), we estimated direct and indirect effects through a path diagram linking maternal birthweight, education, age at childbirth, and pregnancy-related factors such as preterm birth and multiple pregnancies. Paternal factors were also examined.

Maternal birthweight positively influenced both maternal education and child birthweight. However, maternal education had no direct effect on child birthweight and showed indirect negative effects through older maternal age and multiple pregnancies. Paternal education and age at childbirth showed weaker effects compared to maternal factors.

Our findings show birthweight is transmitted across generations, but maternal education does not necessarily strengthen this intergenerational transmission. Our analysis indicates that its indirect pathway-through delayed childbirth among highly educated women-increases risks to infant health. Addressing these risks will require comprehensive investments in maternal health, maternity and workplace support, fertility assistance, and education policies.